Functions of vitamin A, B, C, D, E

What are Vitamins?

A vitamin is a vital substance needed in small quantities for growth and good health. Vitamins are vital body regulators. They may be defined as a group of potent organic compounds that are present in food and are essential in minute quantities for specific functions of growth, maintenance, and reproduction. Most of them are not synthesized by the body and must be supplied through diet. The word vitamin was coined by Casimir Funk who discovered a water-soluble substance in rice polishing which prevents beriberi. He described this compound as vital amine, hence he named the substance vitamins.

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Functions of Vitamin A

  1. Vision: It maintains a clear cornea. As a component of rhodopsin, a protein in eyes that allows seeing in low light conditions.

  2. Cell Differentiation:  In the form of retinoic acid, it is put to work in normal cell differentiation, this process through which stem cells develop into highly specific types of cells with unique functions.

  3. Growth: Retinol is needed for the synthesis of certain glycoproteins, which are required for growth.

  4. Immunity: It is required to maintain the normal health and function of epithelial layers, which provide the first line of defense against invading microorganisms.

Functions of Vitamin B 

  1. VitaminB1 - is one of the most important components among the vitamins which participate as a coenzyme in several metabolic reactions.

  2. Vitamin B2 - helps in the body break down of fats, drugs, and steroid hormones.

  3. Vitamin B3 - is essential for normal functions of the skin, intestinal tract, and the nervous system.

  4. Vitamin B6 - aids in lipid metabolism and in iron utilization for the maturation of RBC. 

  5. Vitamin B6 -  is essential for reproduction in animals.

  6. Vitamin B12 - is involved in biochemical processes essential for DNA synthesis and therefore growth and division of cells.

Functions of Vitamin C 

  1. Enzymatic Role: It acts as an electron donor for 11 enzymes. Many of these enzymes participate in many biochemical functions in the body.

  2. Collagen Synthesis: It plays an important role in the process of formation of collagen that helps in binding agents for the body cells.

  3. Antioxidants Action: It acts as a powerful antioxidant as it can donate a hydrogen atom and form a relatively stable anciently free radical.

  4. Bone Formation: Ascorbic acid is vital for bone formation. 

  5. Wound Healing: it helps in wound healing as it helps in collagen information.

  6. Reduction of Risk of Cancer: It acts as an antioxidant that prevents the action of free radicals. Thus, Vitamin C decreases the risk of cancer. 

Functions of Vitamin D 

  1. Bone Formation: It helps deposition in the bones, probably of mineralized rather than amorphous calcium phosphate by supplying Ca & P in proper concentration to the bone matrix.

  2. Ca Metabolism: It helps in the proper metabolism of Ca in the body, not only as a controller of absorption but as a regulator in those processes where Ca plays an important role. 

  3. Hormonal role of Vitamin D: It is considered as a hormone since its functions are similar to that of some hormones. Vitamin D acts at distant, target organs like the intestine and bones like hormones. It together with parathyroid hormone and calcitonin,  acts in maintaining a number of metabolic processes.

Functions of Vitamin E 

  1. Heart Disease: VitaminE reduces the risk of coronary heart disease since they prevent free radical damage to blood vessels and coronary cells mainly.

  2. Lipofuscin: It prevents the formation of this brown-colored pigment and thus delays aging. 

  3. Immunity: Maintains cellular immunity. It helps in functioning the T-cells. 

  4. The action of Selenium: Selenium is a trace-element which also acts as an antioxidant. Selenium and Vitamin E together function as antioxidants protecting the body against free radical damage.

Fun Facts

  • Vitamins are required in a small quantity to perform a certain metabolic function or to prevent an associated deficiency disease in the body.

  • Vitamins cannot be synthesized by the body and must, therefore, be supplied through food. 

  • According to solubility, Vitamins are classified into two categories (I) Fat-soluble vitamins e.g: A, D, E, K. (II) Water-soluble vitamins e.g: Members of B complex family, vitamin C. 

  • Fat-soluble vitamins are not destroyed by ordinary cooking methods. 

  • Fat-soluble vitamins are stored in the body and at times, cause toxicity when supplied in excess (hypervitaminosis). 

  • Fat-soluble vitamins are not absorbed if mineral oil is present in the intestine.

  • Excess intake of Water-soluble vitamins does not result in hypervitaminosis since these can be excreted through urine and other water routes of excretion. 

  • Water-soluble vitamins are affected by preparation practices. 

  • Deficiency of any kind of vitamin leads to a disease e.g deficiency of VitaminA causes Night Blindness.

  • The ever Vitamin was discovered in 1912.

FAQ (Frequently Asked Questions)

1. What are the sources of Vitamin D?


  • Food Source -  Vitamin D is found in egg yolk, milk, butter, livers of all animals, fish, liver oil, etc. 

  • Cutaneous Source - Human beings produce Vitamin D from sunlight with the help of 7-dehydrocholesterol present in the skin. If a person is dark-skinned then vitamin D synthesis is less due to the presence of melanin pigment. Direct rays of the sun are needed for vitamin D production and so production is lower in winter. Elder people synthesize less vitamin D than young. The use of sunscreen lotions, dark glass windows, etc. can prevent vitamin D synthesis.

  • Other Sources - vitamin D is produced in the placenta and other important issues of the body.

2. How can the deficiency of VitaminA result in the eyes?

Ans. In eyes, Vitamin A deficiency can be seen commonly as-

  • Night Blindness: This is a condition in which an individual is unable to see clearly in dim. 

  • Conjunctiva Xerosis: This conjunctiva becomes dry and thickened, wrinkled, and pigmented. A peculiar smoky appearance is given to the conjunctiva by the pigmentation.

  • Bitot's Spot: This is a condition where spots develop on the eyes. 

  • Corneal Xerosis: When dryness spreads to the cornea there is dull, hazy, lustreless appearance due to keratinization. This leads to dryness and a lack of vision ultimately.

  • Keratomalacia: In this condition, there is a softening of the cornea. 

  • Xerophthalmic Fundus: This is the last stage of eye damage due to Vitamin A deficiency that cannot be treated at all.